Thermoplastic pump plunger having spiral threads and method of making same

ABSTRACT

Adjacent plunger sections having alternate right and left hand spiral threads are loosely fitted on a cylindrical mandrel, one end of which has a threaded valve cage with a ball and seat therein, a shoulder section being threadedly engaged with the other end of the mandrel. The plunger sections are compressed by further increasing rotational pressure to the threaded shoulder section. Plunger sections are essentially nylon (polyamide) having a fiber glass filler material. Because of the creep of the material, end compression is applied in an amount which causes a squeeze of approximately 1/32 inch per foot of plunger section to purposely induce creep in the manufacturing process. After apprxoimately twenty-four hours, during which the material creeps about 75 percent of its one year creep, the plunger assembly is centerless ground to the desired outside diameter. In addition to the plunger sections being alternately right and left hand threaded, each section has its end portion unthreaded. The unthreaded end portion provides for pressure change and also a space for sand to fall out. The use of the unthreaded section and the alternately changing thread directions causes flow reversals and turbulent flow conditions which reduce slippage rate and increase the efficiency of the pump. The alternate right and left hand portions reduce the torque in the system and also reduce the flow rate through the spiral by causing direction changes.

United States Patent [1 1 Douglas 1 [21] Appl. No.: 235,898

[52] US. Cl. 29/l56.4 R, 29/446, 29/445,

264/162 [51] Int. CI B28b 17/02 [58] Field of Search 29/419, 446, 452, 445,

29/l56.63, 156.5 R, 156.4 R; 156/154, 288; 51/324; 264/162 [56] References Cited UNITED STATES PATENTS 1,698,481 1/1929 Mummert 29/156.63 2,511,700 6/1950 Duester 51/324 1,458,248 6/1923 Seifert 29/l56.63 1,494,913 5/1924 Hughes. 29/l56.63 1,386,997 8/1921 Elliott i 29/l56.63 2,394,721 2/1946 Simmons et a1, 156/154 2,903,390 9/1959 Kojima 156/154 3,186,271 6/1965 Kaiser 29/557 7 3,146,725 9/1964 Harris 417/554 FOREIGN PATENTS OR APPLICATIONS 1,029,644 5/1958 Germany 29/l56163 4,140 5/1909 Great Britain 29/l56.63

Primary ExaminerCharles W. Lanham Assistant Examiner-D. C. Crane Attorney, Agent, or Firm-John N. Hazelwood; William E. Johnson, .Ir.; Michael J. Caddell [4 1 Apr. 2, 1974 [57] ABSTRACT Adjacent plunger sections having alternate right and left hand spiral threads are loosely fitted on a cylindrical mandrel, one end of which has a threaded valve cage with a ball and seat therein, a shoulder section being threadedly engaged with the other end of the mandrel. The plunger sections are compressed by further increasing rotational pressure to the threaded shoulder section. Plunger sections are essentially nylon (polyamide) having a fiber glass filler material. Because of the creep of the material, end compression is applied in an amount which causes a squeeze of approximately l/32 inch per foot of plunger section to purposely induce creep in the manufacturing process. After apprxoimately twenty-four hours, during which the material creeps about 75 percent of its one year creep, the plunger assembly is eenterless ground to the desired outside diameter.

In addition to the plunger sections being alternately right and left hand threaded, each section has its end portion unthreaded. The unthreaded end portion provides for pressure change and also a space for sand to fall out. The use of the unthreaded section and the alternately changing thread directions causes flow reversals and turbulent flow conditions which reduce slippage rate and increase the efficiency of the pump. The alternate right and left hand portions reduce the torque in the system and also reduce the flow rate through the spiral by causing direction changes.

8 Claims, 2 Drawing Figures THERMOPLASTIC PUMP PLUNGER HAVING SPIRAL THREADS AND METHOD OF MAKING SAME RELATED APPLICATION U.S. application Ser. No. 236,045, filed Mar; 20, 1972, entitled PUMP PLUNGER HAVING ALTER- NATE RIGHT AND LEFT HAND SPIRAL THREADS.

BACKGROUND OF THE INVENTION This invention relates generally to pumps, and it relates more particularly to pistons or plungers for reciprocating pumps.

Reciprocating pumps have long been used to pump oil from wells in the earth, for example as is illustrated and described in U. S. Pat. No. 3,146,725 to J. W. Harris, assigned to the assignee of the present invention. Such pumps are basically of two types, the first wherein the barrel of the pump having a standing valve is anchored to the well casing and a moving plunger having a traveling valve therein reciprocates within the barrel by action of a sucker rod which extends from the plunger to the earths surface. The second type pump has the plunger anchored and the barrel is caused to reciprocate by the sucker rod. The plunger material is generally made of metal or perhaps of rubber or other resilient material. However, I have discovered that in use of the pumps already known in the art, that there frequently is excessive wear on either the plunger section or the barrel section and that frequently such pumps tend to stick or hang up.

It is therefore the primary object of the invention to provide a new and improved pump plunger assembly which has an increased sealing capability while reducing the likelihood of sticking or hanging up within the It is yet another object of the invention to provide a new and improved method of manufacturing a thermoplastic pump plunger wherein the disadvantages of material creep are vastly reduced.

The objects of the invention are accomplished, generally, by the use of a thermoplastic plunger material which is held under compression to induce creep of the material prior to its being ground to size to increase the sealing characteristics of the plunger assembly and to diminish the adverse effects of material creep.

These and other objects, features and advantages of the present invention will be more apparent after a reading of the following detailed specification and drawing, in which:

FIG. 1 is a pictorial illustration of the plunger assembly according to the present invention; and

FIG. 2 is another view, partly in cross section, of the plunger assembly according to FIG. 1.

Referring now to the drawing in more detail, especially to FIG. 1, there is pictorially illustrated a pump plunger assembly according to the present invention, referred to generally by the reference numeral 10. The assembly is shown as having a valve assembly 11 threadedly engaged at one of its ends and a shoulder assembly 12 threadedly engaged at the other of its ends. Located intermediate the valve section 11 and the shoulder assembly 12 are a plurality, for example, four, plunger sections l3, l4, l5 and 16, each of which has a nonthreaded end portion, for example as shown at 13a and 13b and a center portion which has a spiral thread. The adjacent sections are alternately right and left hand threaded for reasons as set forth hereinafter. The shoulder assembly 12 has a reduced diameter external threaded member 17 for threadedly engaging the sucker rod assembly 18 illustrated in FIG. 2.

Referring now to FIG. 2, there is illustrated in greater detail, and partly in cross section, the pump plunger assembly of FIG. 1.

Referring now to FIG. 2, the traveling valve assembly 11 comprises a cage, indicated generally at 20, the cage including an internally threaded connector member 21 which is screwed onto a reduced diameter lower end portion 22 of the mandrel 23 having a longitudinal passage 24 therethrough. The cage 20 has an upper end wall 25 and extending upwardly from wall 25 are a pair of flow passages 26 and 27 to provide fluid communication between the passage 24 and the flow passage 28 connected to the valve seat 29. Within the cage 20 is a movable valve member or ball 30 which is normally seated on the seat 29. The wall 25 of the valve cage is spaced upwardly from the ball 30 to permit upward movement of the ball so that fluidmay flow from the passage 28 into the longitudinal passage 24 by way of the fluid passages 26 and 27.

The elongated, ring-like plunger sections 13, 14, 15 and 16 are slideably fitted upon the cylindrical mandrel 23, the end portion 13a of the plunger section 13 being in an abutting relationship to the shoulder 31 of the valve assembly 11. During the fabrication process of the pump plunger assembly according to the invention, the valve assembly 11 is first threadedly engaged with the threaded section 22 of the mandrel 23, after which the plunger sections 13, l4, l5 and 16, are slideably placed on the cylindrical center portion of the mandrel 23. At this stage in the fabrication process, the plunger sections are fairly loose fitting on the mandrel 23. The threaded shoulder section 12 is then threadedly engaged with the reduced diameter threaded section 32 of the mandrel 23. The shoulder assembly 12 is continually threaded onto the threaded section 32 until the shoulder 33 of the assembly 12 is in an abutting relationship with the end portion 16b of the plunger section 16. Additional torque is applied to the shoulder assembly 12, thus applying a compressive force to the plunger sections 13, 14,15 and 16. Due to the nature of the thermoplastic materials used in the plunger sections 13, l4, l5 and 16, the compressive force applied to the ends of the sections causes the material to creep 1 outwardly. I initially found that there should be a compressive force which squeezes each plunger section by at least l/64 inch per one foot of plunger length to ensure an end seal. However, following additional work I determined that the creep of the material can be controlled more if the end compressive force was increased to squeeze each section l/32 inch per one foot of plunger length. This compressive force serves two functions. By compressing the plunger sections, an end seal results between the valve assembly 11 and the end 13a of the plunger section 13. An end seal also results between the adjacent ends of sections 13 and 14, between the sections 14 and 15, between the sections 15 and 16, and between the end sections 16b and the shoulder assembly 12. In addition to providing improved end seals, the induced creep of the material substantially eliminates additional creep of the material after the pump is placed in service in a producing oil well. As will be explained hereinafter, nylon, the preferred plunger material with approximately 60 percent fiber glass filler, creeps approximately 75 percent of what would normally be one yearss creep in twenty-four hours when under such compression. 1n the fabrication process, after the end squeeze has been applied for approximately twenty-four hours, the plunger assembly is placed in a conventional centerless grinding machine to reduce the outside diameter of the plunger sections to the desired figure.

After the centerless grinding step, the threaded end portion 17 is threadedly engaged with the sucker rod assembly 18 which has fluid passages 40 and 41 to provide fluid communication between the longitudinal bore 24 and the well bore above the pump.

Although not illustrated, the pump plunger assembly described with respect to FlG.s l and 2 can be used with any conventional pump barrel, for example as is illustrated and described in the aforementioned .l. W. Harris Pat. No. 3,146,725. The plunger assembly 10 is reciprocated within the barrel or cylinder (not illustrated) by upward and downward movement ofa string of sucker rods connected to the earths surface. Solid particles which might pass between the plunger and the barrel of a pump during the pumping action will not build up because, when the particles pass by a section of the grooves in the plunger sections 13, l4, l5 and 16, they fall or move into the groove and pass freely through it. The ungrooved end sections between the spiral grooves allows room for the sand or solid particles to fall out. This provides a self cleaning action for the plunger and prevents sticking of the pump. The unthreaded end portions also provide a pressure change in addition to providing space for the sand to fall out. In addition, the use of the unthreaded portions in conjunction with the alternating of the right and left hand spiral threads causes flow reversals and turbulent flow conditions which reduces the slippage rate and increases the efficiency of the pump. Furthermore, the threaded spiral also lubricates the barrel internal diameter to reduce friction and wear. However, it should be appreciated that the apparatus according to the invention can be fabricated without the grooved sections, or can be fabricated with a continuous groove as illustrated in the Harris patent.

Those skilled in the art will recognize that various materials have been used in fabricating pump plunger assemblies, such as the resilient materials used in the aforementioned .l. W. Harris patent, or the metal piston rings described in U. S. Pat. No. 2,336,803 to J. M. Pratt. However, the various attempts which have heretofore been made with respect to the use of plastic or thermoplastic plunger sections have been highly unsuccessful because of the creep of the material. While such plastic plunger assemblies will operate reasonably well in the laboratory, field tests often indicated that the pumps would stick and hang up, thus resulting in a complete failure of the pump. I discovered, however, that by purposely inducing the creep of the material during the fabrication stages, creep which occurs later within the oil well could be kept to a minimum.

During the search for a suitable thermoplastic, I tested many materials prior to discovering the need for the induced creeping step. The materials used in my findings were as follows:

5 l. Nylatron GS. This is a type 6/6 nylon with 5 per- 6 cent molydisulfide made by the Polymer Corporation. Many laboratory and field tests were conducted with this material. All pumps using this material failed due to plungers sticking caused by material creep due to pressure load, moisture absorption and thermal expansion.

2. Zytel 31. This is a type 6/10 nylon made by Du- Pont. One pump was laboratory tested using this material. Zytel 31 was used because the material had lower moisture absorption and thermal expansion than the Nylatron GS. This pump also stuck due to creep caused by the pressure load and moisture absorption.

3. Zytel 7010-13. This is a type 6/6 nylon with 13 percent fiber glass filler made by DuPont. Laboratory tests of this material indicated an increase in time before sticking. However, this plunger stuck due to creep and moisture absorption.

4. Zytel 7010-33. This is a type 6/6 nylon with 33 percent fiber glass filler made by DuPont. This material was tested after boiling in water for eleven hours to moisture condition the material so that the size would not change due to further moisture absorption during testing. This material did not stick during laboratory testing. However, pumps were field tested using this procedure and these pumps stuck due to creep and thermal expansion of the material.

5. Zytel 7040-33. This is a type 6/6 nylon material 7 with 33 percent fiber glass filler which has been modified so that the material retains better strength when moisture saturated. A pump was not tested using this material because I felt that even though this is an improved material, it was not good enough to overcome the creep and thermal expansion problems.

6. Noryl GFN-3. This is a modified polyphelene oxide with 30 percent fiber glass filler made by General Electric Company. Pumps using this material work adequately in the laboratory. However, this material dissolved when tested in actual oil wells due to the aromatics in the crude oil.

7. Lexan 40 percent. This is a polycarbonate material with 40 percent fiber glass filler made by General Electric Company. Pumps using this material were laboratory and field tested. 1 found that the wear properties of this material were inadequate.

8. Zytel 7710-43. This is a type 6/12 nylon with 43 percent fiber glass material made by DuPont. This material tested adequately in the laboratory but failed later due to moisture, thermal expansion and creep.

9. Ryton. This is an experimental polyphelene sulfide with 40 percent fiber glass filler made by Phillips Petroleum Company. This material has very good properties in dealing with moisture absorption and creep. However, the wear properties are very bad. This material was also tested with 55 percent fiber glass filler in an attempt to obtain better wear properties but this also failed.

10. Nylon 6/6 -40-2 1/2. This is a nylon 6/6 with 40 percent fiber glass filler and 2 H2 percent molydisulfide made by the Polymer Corporation. All of the pumps using this material stuck due to moisture absorption and thermal expansion.

11. Nylon 6/12-50. This is a nylon 6/12 with 50 percent fiber glass filler supplied by the Fiberfil Corporation. The material worked adequately in the laboratory. However, the pumps tested in the wells with this material had some moisture absorption and thermal expansion problems when the pump plungers were run with a 0.002 inch fit.

12. Nylon 6/10-60. This is a 6/10 nylon with 60 percent fiber glass filler supplied by the LNP Corporation. This material has performed best of those tested.

6. is reciprocated, those in the art will readily appreciate that the same principles can be applied to the use of a plunger assembly which is anchored and which is used 13. Nylon 6/12-60. This is a 6/12 nylon with 60 perglass filler premixed into the nylon. The 6/6, 6/10 and 6/12 designations are the industry accepted grade description of different nylons.

As can readily be seen from the aforedescribed examples, the nylon 6/10 and nylon 6/12, each with approximately 60 percent fiber glass filler, provides far superior results in fabricating the plunger sections for use in oil well'pumps. These combinations of materials, in conjunction with the use of a compressive force to purposely induce creeping of the material for a predetermined time, for example twenty-four hours, prior to the grinding of the section to the desired outside diameter, results in a far superior and vastly improved perform ance of oil well pumps.

Although I prefer that the nylon material be used with a fiber glass filler, other thermoplastics will serve an adequate purpose, for example the aforementioned Nylatron GS, Zytel 31, Zytel 7010-13, Zytel 7010-33, etc., when used with the aforementioned fabrication process of subjecting the thermoplastic material to compression prior to the grinding of the material.

Thus it should be appreciated that there has been illustrated and described herein the. preferred embodiments of the present invention. However, modifications will be obvious to those skilled in the art from a reading of the foregoing detailed specification. For example, while the preferred embodiment has been illustrated as being directed to a pump plunger assembly wherein the barrel of the pump would be stationary and the plunger in conjunction with a traveling barrel.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 4

l. A method of fabricating a pump plunger, comprising the steps of:

placing at least one cylindrical, tubular, thermoplastic plunger section on a cylindrical, tubular mandrel having a longitudinal bore therethrough; applying compression to the ends of said at least one section for a predetermined time, whereby the outside diameter of said section is increased; and reducing the outside diameter of said at least one section while said at least one section remains under compression after said predetermined time.

2. The method according to claim 1 wherein said reducing step comprises the centerless grinding of said at least one section.

3. The method according to claim 1 wherein said predetermined time is approximately twenty-fou'r hours.

4. The method according to claim 3 wherein said at least one thermoplastic section comprises a member of the polyamide family.

5. The method according to claim 4 wherein said section also includes a fiber glass filler material.

6. The method according to claim 5 wherein said fiber glass filler material comprises approximately 60 percent by weight of the said at least one section.

7. The method according to claim 5 wherein the compressive force applied to the ends of said at least one section is adequate to reduce the length of said at least one section by an amount equal to at least 1.64 inch per foot of plunger section.

8. The method according to claim 5 wherein the compressive force applied to the ends of said at least one section is adequate to reduce the length of said at least one section by an amount equal to at least 1/32 inch per foot of plunger section. 

1. A method of fabricating a pump plunger, comprising the steps of: placing at least one cylindrical, tubular, thermoplastic plunger section on a cylindrical, tubular mandrel having a longitudinal bore therethrough; applying compression to the ends of said at least one section for a predetermined time, whereby the outside diameter of said section is increased; and reducing the outside diameter of said at least one section while said at least one section remains under compression after said predetermined time.
 2. The method according to claim 1 wherein said reducing step comprises the centerless grinding of said at least one section.
 3. The method according to claim 1 wherein said predetermined time is approximately twenty-four hours.
 4. The method according to claim 3 wherein said at least one thermoplastic section comprises a member of the polyamide family.
 5. The method according to claim 4 wherein said section also includes a fiber glass filler material.
 6. The method according to claim 5 wherein said fiber glass filler material comprises approximately 60 percent by weight of the said at least one section.
 7. The method according to claim 5 wherein the compressive force applied to the ends of said at least one section is adequate to reduce the length of said at leaSt one section by an amount equal to at least 1.64 inch per foot of plunger section.
 8. The method according to claim 5 wherein the compressive force applied to the ends of said at least one section is adequate to reduce the length of said at least one section by an amount equal to at least 1/32 inch per foot of plunger section. 